The field of hydraulic systems, particularly with reference to circuits for controlling a plurality of actuators suitable to drive machines of various kinds, generally uses switching valves of the shuttle type provided with a compensating element arranged downstream. This technical solution is disclosed for example in U.S. Pat. No. 5,579,642. This compensating element is designed to keep as constant as possible the pressure drop across the control valve of the hydraulic actuator: this allows to operate the actuator with the chosen behavior. In such a case, the flow-rate delivered to the chambers of the actuator in fact depends exclusively on the passage section, which can be changed by the operator by way of the traditional means.
These switching valves are first of all typically associated with circuits for transmitting the load signal to the compensating elements; such circuits are designed to draw, by means of adapted selection valves, the highest load signal that is present in the various uses. This of course entails a certain constructive complication, which is often too expensive.
As an alternative to this, check valves are used which are directly integrated in the shuttle of the compensating element (as disclosed for example in U.S. Pat. No. 5,305,789), which in any case require the fitting of a so-called compensated “bleed-off” (which in the particular field is also known as “bleed”), which comprises a flow regulator.
A further alternative is constituted by the use of check valves fitted in parallel with respect to the compensating element, which is associated with a bleed-off.
Even these solutions, which in various situations have been optimized, are all characterized by high constructive complexity, which recommends against their use both as regards production costs and as regards installation and subsequent maintenance.
Secondly, moreover, in traditional applications the load signal is typically connected to the discharge by means of a so-called compensated bleed-off, which therefore entails installing additional hydraulic components, which considerably increase the complexity of the system.
Thirdly and finally, the load signal is usually drawn from the so-called bridge of the switching valve, and this fact entails a distinctly bulky design in the upper part of the component: in some applications, this is particularly disadvantageous.
EP-A-0 368 636 and DE 39 12 390 disclose hydraulic control systems with directional control valves having a combination of elements as set forth in the pre-characterizing portion of the appended claim 1.